Out Of 3 Logic - Siemens 7SR12 Argus Manual

polarising reference voltage is set to 0deg and the current phase angle is measured with respect to this
reference.
Alternatively, the instrument can be checked at the 4 points marked a,b,c & d on Figure 2-1 only.
Lag (point C)
Pick-up
MTA MTA-85
Phase A
Phase B
Phase C
A
B
b
0
+180
0
+210
V
C
+240
Figure 2-1
5. With the instrument reading 'Fwd' or 'Rev', reduce the voltage until the element resets. Record the minimum
phase-phase operate voltage.
Minimum Voltage Setting
2.1.1

2 out of 3 logic

Ensure that at least 1 Phase Overcurrent element is set to Directional. Apply balanced nominal voltage. Apply
current at a level above the 50/51 setting on phase A only at the characteristic angle for forward operation,
normally 45º lagging. Ensure no Directional Phase Overcurrent element operation occurs. Note that non-
directional Phase Overcurrent and Non-direction Earth Fault elements may operate unless disabled.
Repeat the test with Phase A current as above but also with equal current in the B phase at 180º to that in the A
phase.
1 phase current
No 50/51-n Operation
©2017 Siemens Protection Devices Limited
Forward
Lead (point A)
Drop-off Pick-up
MTA+85
V
A
0
+90
a
0
+60
I
A
FWD
V
BC
C
REV
D
0
d
0
+270
Directional Phase Fault Boundary System Angles
7SR11 & 7SR12 Commissioning and Maintenance Guide
Lead(point B)
Drop-off Pick-up
MTA-85
With balanced 3-phase system quantities:
Adjust the phase angle of the currents
relative to the voltages:
0
+30
Verify directional pick-up and drop off at
points A, B, C and D
0
0
Alternatively,
Verify correct directional indication at points
c
a, b, c and d (C.A +75
V
B
Measured
2 phase current
50/51-n operation
Reverse
Lag (point D)
Drop-off Pick-up Drop-off
MTA-85
0 0 0 0
, +95 , -75 , -95 )
Chapter 6 Page 13 of 72